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@greatgodoffire 135mm is a good focal length to get started in AP. It is more forgiving and allows you to do reasonably long exposures without autoguiding. If your current EQ mount can track on the RA axis, I'd recommend you give this a try before buying anything.

In AP, a good goto mount is probably the most important piece of gear to buy. With focal lengths ~200mm and above, autoguiding is required to get long sub-exposures without star trailing, and a goto mount is required for autoguiding. It also allows dithering (move the framing just a little bit between exposures) which helps significantly reduce fixed pattern noise from the camera sensor.

Once you have a good mount, you can consider APO scopes in the 250-400mm focal length range like the WO Redcat 51 or the Askar FRA400 (I have the FRA400 and it is AMAZING).